1. Field of the Invention
The present invention relates to an apparatus and method for controlling the start of combustion in an compression engine, and more particularly to an apparatus and method for controlling the start of combustion in an homogeneous charge compression engine by controlling the pressure differential across an intake valve.
2. Description of the Related Art
Homogenous charge compression ignition (HCCI) engines are an attractive alternative to conventional diesel or spark ignited engines because of their potential for producing low NOx and particulate emissions as well as their high thermal efficiency. Combustion is typically achieved in an HCCI engine by compressing a substantially homogeneous intake air/fuel charge until it auto-ignites. The combustion of the substantially homogeneous intake charge is typically characterized by generally uniform, low-temperature, fuel-lean reactions.
One of the principal challenges of HCCI engines is how to control the start of combustion during a given intake cycle. In spark-ignition and diesel engines, the start of combustion is directly controlled. For example, in a spark-ignition engine, the start of combustion is controlled by the sparking of the spark plug. In a diesel engine, the start of ignition is controlled by the beginning of fuel injection. In an HCCI engine, however, the intake charge auto-ignites and, thus, there is no direct control of the start of combustion. Instead, the start of combustion is determined by the auto-ignition chemistry of the intake charge and the temperature and pressure of the intake charge near top-dead-center (TDC) of the compression stroke.
Several approaches for controlling the start of combustion in a HCCI engine have been suggested. For example, it has been suggested that the start of combustion can be controlled by varying the properties of the fuel and/or the air/fuel ratio. This method relies on adjusting the reactivity of the intake charge. Accordingly, the start of combustion can be advanced by increasing the reactivity of the intake charge and the start of combustion can be delayed by decreasing the reactivity of the intake charge.
It has also been suggested that the start of combustion can be controlled by adjusting the intake air temperature. Increasing the intake air temperature tends to increase the temperature of the intake charge near top-dead-center. This tends to advance the start of combustion. Similarly, decreasing the intake air temperature tends to delay the start of combustion.
However, to date, these methods for controlling the start of combustion in HCCI engines have been largely unsatisfactory. Accordingly, a need exists for an improved method of controlling the start of combustion in an HCCI engine.
One aspect of the present invention is the recognition that the start of combustion in an HCCI engine can be controlled by controlling the pressure differential between intake valve port and the combustion chamber when the intake passage is in communication with the combustion chamber (i.e., when the intake valve lifts away from the intake valve port). Specifically, an aspect of the invention involves the recognition that by increasing the pressure differential across the intake valve the enthalpy and kinetic energy of the intake charge in the combustion chamber can be increased.
As the kinetic energy dissipates, the temperature of the intake charge increases during the compression stroke. This results in increased temperatures around top-dead-center of the compression stroke. Moreover, the start of combustion in a HCCI engine depends mainly upon the temperature of the intake charge around top-dead-center of the compression stroke. Accordingly, the start of combustion can be controlled by controlling the pressure differential across the intake valve.
Accordingly, another aspect of the present invention involves a method for operating an internal combustion engine. The engine includes at least one combustion chamber formed by at least a first member and a second member that moves relative to the first member. The second member is coupled to an output shaft such that movement of the second member causes the output shaft to rotate. An intake port is in communication with the combustion chamber and an intake passage. The intake port and is opened and closed by an intake valve that is actuated by a valve actuating system. A fuel supply system and air supply system are configured to provide a substantially homogeneous air/fuel charge to the combustion chamber. A control system configured to control the valve actuating system. A substantially homogenous air/fuel charge is formed. At least the air of the air/fuel charge is introduced into the combustion chamber through the intake port. When the air/fuel charge auto-ignites is controlled by adjusting a pressure differential between the intake port and the combustion chamber when the intake passage is in communication with the combustion chamber. The air/fuel charge is compressed and auto-ignited due to the compression of the air/fuel charge.
Another aspect of the invention involves an internal combustion engine that includes at least one combustion chamber formed by at least a first member and a second member that moves relative to the first member. The second member is coupled to an output shaft such that movement of the second member causes the output shaft to rotate. An intake port is in communication with the combustion chamber and is opened and closed by an intake valve that is actuated by a valve actuating system. A fuel supply system and air supply system are configured to provide a substantially homogeneous air/fuel charge, which comprises mixed air and fuel, to the combustion chamber. A control system is configured to control the valve actuating system. The engine further includes means for controlling when the air/fuel charge auto-ignites due to compression of the air/fuel charge in the combustion chamber.
Yet, another aspect of the present invention involves an internal combustion engine comprising of at least one combustion chamber formed by at least a first member and a second member that moves relative to the first member. The second member is coupled to an output shaft such that movement of the second member causes the output shaft to rotate. An intake port is in communication with the combustion chamber and an intake passage. The intake port is opened and closed by an intake valve that is actuated by a valve actuating system. A fuel supply system and air supply system are configured to provide a substantially homogeneous air/fuel charge, which comprises mixed fuel and air, to the combustion chamber through the intake port. A control system is configured to control the valve actuating system and is furthered configured to control when the air/fuel charge auto-ignites by adjusting a pressure differential between the intake port and the combustion chamber when the intake passage is in communication with the combustion chamber.
All of these embodiments are intended to be within the scope of the invention.